The present invention relates to the field of motion control systems, and, in particular, to sizing and tuning methodologies for implementing motion control systems.
Motion control in the field of automation generally refers to controlling the position, velocity or torque/acceleration of machines or loads using some type of device, such as an electromagnetic motor or actuator. Typically, a servo mechanical device (servomechanism) or drive having closed loop feedback is used, which provides error-sensing negative feedback to compensate for deviations in actual motion of the motor while attempting to follow a motion profile. In operation, a drive may power a motor according to a motion profile which, in turn, drives a load. Then, feedback is returned to the drive from the motor, which allows the drive to compensate for errors in the actual motion of the motor, periodically or continuously.
Oftentimes, a motion planner, such as one residing in a motion planner, a programmable logic controller (“PLC”), a PLC with integrated motion planner (“PLC+”), an automation controller, an industrial PC (an x86 PC-based computing platform for industrial applications) or other device, is used to provide an electronic motion profile, or command trajectory, to the drive. The motion planner sends the electronic motion profile to the drive via a common industrial protocol (“CIP”) control network, which is a network suitable for highly reliable and available real-time communication. Control networks commonly used include, for example, ControlNet, DeviceNet, EtherNet/IP, SERCOS, EtherCAT, Profibus and CIP Motion, whose specifications are published and whose protocols are used broadly by a number of manufacturers and suppliers. The motion planner may also send commands via an analog interface, such as +/−10V, or digital pulse train, such as a Step and Direction Interface. Of course, the partitioning of motion control components may vary, such as by industry. In fact, some implementations may provide a PLC, drive and motor in a single package
Typically, separate software tools are used for sizing and selecting motor/drive components, and for configuring, programming and executing the motion control application. Position and velocity control loops in the motion control system may be set by the industrial environment via proportional-integral-derivative (“PID”) controllers and Feed-forward Gains, which may greatly impact the gain and phase response of the system and thus power/energy efficiency. Motion Analyzer, for example, a software tool from Rockwell Automation, Inc., may be used to assist in the sizing and selection of machine components, and RSLogix5000, for example, may be used to configure, program and execute the motion control application.
Sizing calculations are oftentimes performed as “backwards open loop calculations,” meaning that instead of closing the loop to calculate the output and all other internal signals, the output is assumed to follow the input perfectly. Then, back calculations are made from the output to calculate other signals, such as the current and energy required.
However, this does not fully consider the effects of tuning parameters, such as gain values for the PID controller, and the motion profile, and may not account for losses in the system due to these values. For example, lower gain values increase energy efficiency but decrease performance, while higher gain values decrease energy efficiency but increase performance. Also, external disturbances in the system, such as friction, variations according to temperature, and variations in manufactured components often lead to variances that are not fully considered.
Consequently, a drive and motor may require greater current (and power or energy) than necessary to overcome such variances and external disturbances. This, in turn, leads to excess power/energy consumption, excess heat and inefficiency. A motion control software tool that estimates and improves power/energy efficiency while maintaining performance is needed. In addition, a motion control software tool that enables a user to further define their motion control application to allow maximum power efficiency to be realized with minimized cost and machine footprint is needed.